a) Field of the Invention
The present invention relates to a conveyor belt and a method of making the same, and more particularly such a conveyor belt and method utilizing, as a parting material, polymeric material which becomes part of the finished surface of the conveyor belt.
b) Background Art
A common method of manufacturing a conveyor belt is to provide a body of material in an elongate belt configuration having upper and lower surfaces with the material of the conveyor belt comprising at least in large part rubber and/or synthetic rubber. The conveyor belt body is positioned between upper and lower heated platens, which are then pressed against the conveyor belt body to cause vulcanization of the rubber and/or synthetic rubber (hereinafter to be referred to as "rubber"). Quite commonly, reinforcing material is provided between layers of the rubber material that is to form the body, such as steel cables, fabric or other material. Further, the layers of the belt body can differ in composition, such as an inner layer or layers being made of a cushioned rubber material, and the outer layers being of a cover rubber material.
It is usually necessary to provide some sort of parting agent at the upper and lower surfaces of the body which is positioned between and pressed by the platens, so that upon completion of the application of heat and pressure to cause vulcanization of the rubber material, the platens can be properly separated from the belt section that has just been formed. One common method of doing this is using a chemical or a fabric like material to provide a release and prevent sticking. Chemical releases can be in the form of a powder (e.g. talc), a liquid (e.g. silicone spray) or a solid (paraffin waxes). These are applied to the top and bottom surfaces of the belt. Also, as a parting agent, fabric materials can be utilized (e.g. a fine strand square woven polyester cloth). The cloth is removed after vulcanizing. Also, light random wisps of synthetic or natural material (e.g. nylon or cotton-like "angel hair") is used. One type of such material is manufactured under the trademark "CEREX". This material which is very thin is vulcanized into the belt surface and becomes part of the belt).
There are a number of significant considerations relating to the character of the upper and lower surface portions of the belt. One such consideration is the appearance of these upper and lower surfaces. It often happens that during the vulcanizing process where the platens are applied against the belt section, the color, shading or texture of the belt surface may become non-uniform so that there are "splotches" of a differing shade and/or color that degrade the appearance of the belt. Also, if the belt has a highly reflective surface (i.e. a mirror-like surface) the splotches become substantially more noticeable than if there is a reflectively soft textured surface.
Another consideration regarding the character of the surface of the belt is its elastomeric qualities. As a loaded belt passes over the support rollers, there is an indentation of the belt surface portion in contact with the rollers. If the surface portion of the belt has poorer elastomeric qualities, then more energy is required to move the belt over the rollers, thus requiring more powerful motors. On the other hand, if the surface portion of the belt recovers from the compression more resiliently, the energy required to move the belt is diminished.
A search of the U.S. patent literature has revealed a number of patents, these being the following:
U.S. Pat. No. 4,744,843 (Lewis) discloses the use of a releasing agent for a conveyor belt. In column 1, line 35 and following the invention is described as follows:
"I have discovered that a polymeric monomer nonwoven fabric made preferably directly from molten polymer as preferably continuous filaments that are entangled and may or may not be bonded at each crossover point can be used as a very satisfactory mold release in molding belts and related materials and the nonwoven fabric becomes a part of the molded article. The resulting molded article has an improved appearance of the article due to the elimination of trapped air or gases and the elimination of mold release build-up with its effect on appearance of the molded article."
U.S. Pat. No. 4,411,947 (Haynhold) shows a conveyor belt having a body of rubber or synthetic materials with steel cable reinforcing. The belt is formed with an elastically deformable cushioning insert which contains air pockets and is embedded in either the upper and/or lower cover layer. The problem toward which this is directed is that the conveyor belt is stressed at the loading location since the material being loaded is usually dropped onto the belt. Accordingly, these air pockets cushion the belt to withstand these impacts. There is a double weave cloth 5 comprising two fabric layers 15 and these are interconnected by the threads 25 to keep them in parallel relationship.
U.S. Pat. No. 2,841,515 (Runton et al) shows a belt made of canvas layers having between the layers a synthetic foam which bonds the canvas layers together. A layer of the foam is also placed on the face of the belt when required for a protective coating to prevent cutting or tearing the belt when hard objects fall on it.
U.S. Pat. No. 2,515,778 (Knowland et al) discloses a belt which is adapted for use in the canning and food handling industry. The body of the belt is made of "rubberized multiple plys vulcanized into a unit and covered with synthetic plastic composition bonded and vulcanized thereto." The layer is of a light color, odorless and resistant to solvents, oils, fats, etc. The plastic composition and a fabric sheet are bonded under pressure and heat to soften the plastic so that it permeates and bonds to the fabric sheets.